Weigh the eggs. Take the same weight in butter, sugar and flour. Beat the butter and sugar together until pale and light in texture. Wash the oranges and add the finely grated rind of 2 and the juice of 1 to the butter mixture. Mix the flour and baking powder and add alternately with the eggs. Beat thoroughly. Bake in a 24cm (91/2in) tin in a moderate oven, 180°C/350°F/gas 4, for 50 minutes approx. Cool the cake and split it in two. Sandwich with the orange butter icing and spread the chocolate icing over the top and sides allowing any excess to run off.
To make the orange butter icing, finely grate the rind of the orange and squeeze out the juice. Beat the icing sugar, butter and orange rind together. Add in enough juice to make the icing a spreading consistency.
To make the chocolate icing, melt the chocolate in the water. Remove from the heat and beat in the butter and then the eggs very thoroughly. Leave to cool and set before icing and filling the cake.